warfarin

Question 1

what is warfarin used for (indications)

Answer 1

• to prevent embolisation (blood clots) in rheumatic heart disease, atrial fibrillation, after insertion of prosthetic heart valve
• treatment and prevention of venous thrombosis and pulmonary embolism
• treatment of transient ischaemic attacks (mini stroke)

Question 2

what are the contraindications for warfarin (+ all vitamin k antagonists)

Answer 2

• use within 48 hours postpartum
• hemorrhagic stroke
• significant bleeding

Question 3

what are the cautions for warfarin

Answer 3

• history of GI bleeding
• hyper/hypothyroidism
• uncontrolled hypertension
• recent ischaemic stroke
• changes in diet (intake of vitamin K)

Question 4

can warfarin be used during pregnancy

Answer 4

should not be given in the 1st trimester. should also avoid in the 3rd trimester

Question 5

is warfarin safe for breastfeeding

Answer 5

yes. Not present in milk in significant amounts and appears safe.

Question 6

how often is the monitoring on warfarin

Answer 6

in the early days of treatment it is daily or on alternate days. After that you can have longer intervals up to every 12 weeks

Question 7

name 2 types of juice that interact with warfarin

Answer 7

• Cranberry juice
• Pomegranate juice

both increase the INR of warfarin = increased anticoagulant effect

note increased INR= increased risk of bleeding

Question 8

how do you know the therapeutic range (dose) of warfarin for a patient

Answer 8

the dose of warfarin depends on the patients INR

Question 9

what are the symptoms of warfarin toxicity

Answer 9

Haemorrhage (bleeding)

Question 10

which conditions have a target INR of 2.5

Answer 10

• deep vein thrombosis or pulmonary embolism
• atrial fibrillation
• cardioversion (target INR should be achieved 3 weeks before cardioversion + continued for 4 weeks after)
• myocardial infarction
• dilated cardiomyopathy

note: target INR is 2.5 (+/- 0.5 units)

Question 11

what condition has an INR of 3.5

Answer 11

• RECURRENT deep-vein thrombosis or pulmonary embolism in patients currently receiving anticoagulation and with an INR above 2

Question 12

what is the INR for Mechanical prosthetic heart valves

Answer 12

There’s no specific INR. Recommended INR depends on:

• type and location of valve
• patient- related risk factors

consider increasing INR or adding antiplatelet drug if embolic events happens during anticoagulation

Question 13

how long does it take for the full anticoagulant effect of vitamin-K antagonists to develop

Answer 13

at least 48-72 hours

Question 14

when would you deem an INR result as satisfactory

Answer 14

if it is within 0.5 units of the target value.

note larger deviations from target value than this mean the dose needs to be adjusted

Question 15

what is the treatment plan if a patient taking warfarin has a MAJOR bleed

Answer 15

• stop warfarin sodium + give phytomenadione (vitamin K1) by slow intravenous injection
• give dried prothrombin complex (factors II, VII, IX, and X); if dried prothrombin complex unavailable, fresh frozen plasma can be given but is less effective

Question 16

what is the treatment plan for all patients taking warfarin if they have an INR of 5-8 and MINOR bleeding

Answer 16

• stop warfarin sodium + give phytomenadione (vitamin K1) by slow intravenous injection
• restart warfarin sodium when INR <5.0

Question 17

when should a patient who has stopped warfarin due to high INR/bleeding restart warfarin

Answer 17

when the INR is less than 5 (<5.0)

Question 18

when is the only time a patient is given phytomenadione (vitamin K1) by mouth using the intravenous preparation orally [unlicensed use]

Answer 18

if the patient has an INR >8.0 but no bleeding

Question 19

what is the treatment if a patient has an INR 5.0-8.0 and NO bleeding

Answer 19

withhold 1 or 2 doses of warfarin sodium and reduce subsequent maintenance dose

Question 20

describe how to manage a patient on warfarin before ELECTIVE surgery

Answer 20

• warfarin should be stopped 5 days before surgery. Give I.V phytomenadione (vitamin K1) orally (unlicensed) the day before surgery if INR >1.5
• if patient is considered high risk, still stop warfarin but use interim therapy (bridging) by using low molecular weight heparin but stop this at least 24 hrs before surgery
• if haemostasis ok, restart normal maintenance dose of warfarin the evening of surgery or the next day

Question 21

what is the treatment plan if a patient on warfarin requires EMERGENCY surgery

Answer 21

• if surgery can be delayed for 6-12 hours, give I.V phytomenadione (vitamin K1) in the meantime to reverse anticoagulant effect
• if surgery can’t be delayed, give I.V phytomenadione (vitamin K1) + dried prothrombin complex. check INR before surgery

Question 22

what is given to reverse the anticoagulant effect of warfarin

Answer 22

I.V phytomenadione (vitamin K1)

note the I.V formulation can be given orally (unlicensed)

Question 23

why might a patient taking warfarin need their warfarin dose reduced if they get an acute infection (including covid)

Answer 23

because acute infections (including covid) can exaggerate the effect of warfarin.

monitor the patients INR to reduce risk of bleeding

Question 24

why should your monitor patients taking vitamin-k antagonists INR every time they start a new medicine

Answer 24

because vitamin k antagonists (e.g warfarin) have a lot of interactions with other medicines (including antibacterials + antivirals) so monitoring at the start of new meds reduces risk of potential interactions

Question 25

name of examples of when patients taking vitamin k antagonists should notify their GP

Answer 25

- symptoms or confirmed covid infection - unwell with sickness/ diarrhoea or lost appetite - have changed their diet, smoking habits or alcohol consumption - taking any new meds or supplements - unable to attend next scheduled blood test

Question 26

why should warfarin patients speak to their doctor if they develop a painful rash

Answer 26

warfarin can lead to calciphylaxis (when calcium accumulates in small blood vessels of skin + fat tissue. leads to infections/ tissue necrosis/ death) * note it is rare and mostly seen in patients with end-stage renal disease*

Question 27

when should a woman postpartum start taking warfarin again

Answer 27

delay warfarin until risk of bleeding is low (usually 5-7 days after birth delivery)

Question 28

how can major diet changes affect anticoagulant control in patients taking vitamin k antagonists name examples of foods high in vitamin k

Answer 28

food containing vitamin k counteracts the effects of vitamin-k antagonists so reduces anticoagulant effect of vitamin-k antagonists. examples of food high in vitamin k: - green leafy vegetables e.g kale, collard greens, broccoli, spinach, cabbage, and lettuce - salads - green tea - kiwi

Question 29

which juice interacts with warfarin to increase the INR

Answer 29

both Cranberry and Pomegranate juice increase the INR of warfarin increase in INR= blood is taking longer to clot so increased risk of bleeding

Question 30

can alcohol consumption affect the anticoagulant effect of warfarin

Answer 30

yes, alcohol consumption (in those who drink heavily) potentially decreases the anticoagulant effect of Warfarin.

Question 31

when is it advised that pregnant women stop taking vitamin k antagonists

Answer 31

stop vitamin k antagonists before the 6th week of gestation to avoid fetal abnormalities warfarin should not be taken in the 1st and 3rd trimester - teratogenic

Question 32

TRUE OR FALSE if a mother has been taking warfarin at the time of birth, their baby should be given immediate prophylaxis with intramuscular phytomenadione (vitamin K1)

Answer 32

TRUE